Typing local variables does not work - results in Error: This Type-Name has no effect

I'm not sure this if this is bug or not, but I wanted to get some feedback on a small test case that I wrote while researching Puppet variable data types. I have a params.pp and init.pp class as follows:

class vartest::params {

  String $param1 = 'teststring'

}

class vartest (

  String $param1 = $vartest::params::param1

) inherits vartest::params {

  notice($param1)

}

I receive the following message when I invoke "puppet apply -e 'include vartest'":

Error: This Type-Name has no effect. A value was produced and then forgotten (one or more preceding expressions may have the wrong form) at /etc/puppetlabs/code/environments/production/modules/vartest/manifests/params.pp:2:3 on node sdp-exercise.vagrant

If I delete the String token from the variable assignment in init.pp, I receive the same message. If I restore that token and then remove the String token from the variable assignment in params.pp, I see the following output from puppet apply:

Notice: Scope(Class[Vartest]): teststring

Notice: Compiled catalog for sdp-exercise.vagrant in environment production in 0.15 seconds

Notice: Applied catalog in 0.01 seconds

I'm just wondering if those errors above are expected and why I can't use the String data type in both classes. It seems like that might be a useful language feature, especially when heavily refactoring code and wanting to make sure inherited variable data types still match what's expected.